1. Field of the Invention
The present invention relates to an optical fiber positioning member used for optically connecting optical fibers to each other.
2. Related Background Art
Optical connectors are usually in use for connecting optical fibers employed in optical communications, whereas optical fiber positioning members such as ferrule and sleeve are used in the optical connectors. Such optical fiber positioning members necessitate a high dimensional accuracy since they are required to carry out positioning of the respective axial centers of optical fibers to be butted against each other at a high accuracy, and also demand a high dimensional stability when they are to be used over a long period of time. At the same time, the optical fiber positioning members are required to have not only a sufficient mechanical strength but also a long-term durability since they are repeatedly attached and detached.
As such an optical fiber positioning member, ferrules obtained by transfer-molding of epoxy resins, which are thermosetting resins, have conventionally been known, for example. However, such ferrules molded from thermosetting resins take time for curing while molding, whereby their productivity lowers.
Therefore, thermoplastic resins have come into use in optical fiber positioning members in order to improve the productivity.
For example, Domestic Republication WO95/25770 discloses a ferrule comprising a resin composition which contains a polyphenylene sulfide resin or the like at a content in the range of 20% to 40% by weight, spherical fine particles of silica or the like at a content in the range of 40% to 60% by weight and whiskers such as potassium titanate whiskers, aluminum borate whiskers, silicon carbide whiskers, silicon nitride whiskers, zinc oxide whiskers, alumina whiskers, graphite whiskers, or the like at a content in the range of 15% to 25% by weight.
On the other hand, Publication WO99/53352 discloses a ferrule comprising a resin composition which contains a polyphenylene sulfide resin, silica particles, and zinc oxide whiskers at a content in the range of 5% to 30% by weight and silicate whiskers at a content in the range of 5% to 30% by weight.
The inventors have studied the prior art mentioned above. As a result, the inventors have found that the above-mentioned prior art has problems as follows.
Namely, though the ferrule disclosed in Domestic Republication WO95/25770 is advantageous in terms of dimensional accuracy since it contains silica particles and whiskers in its resin composition, it may not have a sufficient strength at its parts surrounding guide holes into which guide pins are inserted, so that the parts of ferrule surrounding the guide holes may chip off when the guide pins are inserted into and pulled out of the guide holes. In MPO optical connectors of push-on/pull-off type, in particular, guide pins may be impulsively inserted into guide holes of the ferrule while being shifted or tilted with respect to the guide holes, whereby the parts of ferrule surrounding the guide holes are apt to chip off. As a consequence, the ferrule requires replacement and the like at a relatively early stage, so that it may fail to be used over a long period of time. Also, its dimensional stability cannot be considered sufficient.
Though the ferrule disclosed in Publication WO99/53352 is considered to be advantageous in terms of dimensional accuracy, dimensional stability, mechanical strength, and long-term durability, it is required to further improve these performances.
It is an object of the present invention to provide an optical fiber positioning member which can further improve its dimensional accuracy, mechanical strength, dimensional stability, and long-term durability.
In order to achieve the above-mentioned object, the inventors have carried out diligent studies. Namely, while packing a polyphenylene sulfide resin (hereinafter referred to as xe2x80x9cPPS resinxe2x80x9d), silica particles, and whiskers into a resin composition constituting an optical fiber positioning member, and varying the respective packing amounts of the PPS resin, silica particles, and whiskers, as well as the structure of PPS resin and kinds of whiskers to be packed, the inventors evaluated the dimensional accuracy, mechanical strength, dimensional stability, and long-term durability of the resulting resin compositions. As a result, the inventors have found that the above-mentioned object can be achieved when the respective packing amounts of PPS resin, silica particles, and whiskers are within their predetermined ranges, and a PPS resin having a specific structure and whiskers having a specific form are used as the PPS resin and the whiskers, respectively, thereby accomplishing the present invention.
Namely, the optical fiber positioning member in accordance with the present invention comprises a resin composition containing a PPS resin mainly composed of a linear type PPS resin at a content in the range of 24% to 30% by weight, silica particles at a content in the range of 61% to 67% by weight, and tetrapod-shaped whiskers at a content in the range of 6% to 12% by weight.
In the optical fiber positioning member of the present invention, tetrapod-shaped whiskers have such a low anisotropy that its coefficient of thermal shrinkage at the time of molding has a lower anisotropy, better mold-transferability, and an improved dimensional accuracy as compared with optical fiber positioning members containing not only this kind of whiskers but also other kinds of whiskers (which are fibrous in general) in addition thereto. Also, since the linear type PPS resin itself has a better fluidity as compared with cross-linked type PPS resins and the like, the fluidity of resin composition further improves. Therefore, a pressure is fully transmitted to the whole mold cavity at the time of molding the resin composition including the linear type PPS resin, whereby the density of the resulting optical fiber positioning member increases. Also, the linear type PPS resin has a higher tenacity than the other types of PPS resins do. Consequently, when the contents of silica particles and tetrapod-shaped whiskers are held constant in the resin composition, a higher mechanical strength is obtained in the optical fiber positioning member using the PPS resin mainly composed of the linear type PPS resin. Here, if the content of tetrapod-shaped whiskers is less than 6% by weight, then the effect of combining them does not become apparent, whereby anisotropy occurs in the coefficient of thermal shrinkage, which may generate warps and distortions in the optical fiber positioning member. If the content exceeds 12% by weight, then the reinforcing effect with respect to the PPS resin becomes weaker, whereby the mechanical strength of the optical fiber positioning member lowers. If the content of the PPS resin mainly composed of the linear type PPS resin is less than 24% by weight, then the moldability of the resin composition deteriorates, thereby lowering its dimensional accuracy. If the content exceeds 30% by weight, by contrast, then the reinforcing effects of silica particles and tetrapod-shaped whiskers with respect to the PPS resin become weaker, whereby the mechanical strength of the optical fiber positioning member lowers. If the content of silica particles is less than 61% by weight, then the coefficient of linear expansion of the whole resin composition becomes so high that its dimensional accuracy lowers, and its modulus of elasticity becomes so low that the mechanical strength of the optical fiber positioning member lowers. If the content exceeds 67% by weight, then the fluidity of the resin composition at the time of molding becomes so low that the moldability of resin composition deteriorates, whereby its dimensional accuracy lowers. Also, the resin composition becomes brittle since the content of PPS resin decreases.
Preferably, in the optical fiber positioning member, the silica particles have one relative maximum value in each of particle size ranges of 0.3 to 0.8 xcexcm and 4 to 7 xcexcm in a particle size distribution thereof.
If a relative maximum value exists within each of the above-mentioned two ranges, then it will be advantageous that silica particles having a smaller particle size enter gaps among silica particles having a larger particle size, thereby improving the packing ratio. Also, when the silica particles having the above-mentioned particle size distribution and silica particles in which at least one of the two relative maximum values is out of the above-mentioned ranges are at the same packing ratio, the fluidity of the resin composition improves more in the case with the silica particles having the above-mentioned particle size distribution since the contact resistance between silica particles is lowered.
Preferably, in the optical fiber positioning member, the tetrapod-shaped whiskers are zinc oxide whiskers.
When whiskers having a tetrapod shape (a three-dimensional form obtained by connecting the center of gravity of a regular tetrahedron and its vertices) are used as such, their anisotropy is low, whereby there is a tendency that the resulting member exhibits a lower anisotropy in coefficient of thermal shrinkage at the time of molding, a better mold-transferability, and an improved dimensional accuracy as compared with the case containing other kinds of whiskers.
Preferably, in the optical fiber positioning member, the content of the linear type PPS resin in the PPS resin is 95% to 100% by weight.
If the content of the linear type PPS resin in the PPS resin is less than 95% by weight, then the fluidity of the resin composition decreases, and the uniformity in density of the optical fiber positioning member decreases, whereby its mechanical strength tends to lower.
Preferably, in the optical fiber positioning member, the melting viscosity of the linear type PPS resin at 300xc2x0 C. is 100 to 500 poises.
If the melting viscosity is less than 100 poises, then the molecular weight of the linear type PPS resin is so low that its mechanical strength tends to lower. If the melting viscosity exceeds 500 poises, then the fluidity of the resin composition deteriorates, so that the dimensional accuracy tends to lower.
Preferably, in the optical fiber positioning member, the average particle size of silica particles is 0.2 to 7 xcexcm.
If the average particle size is less than 0.2 xcexcm, then the fluidity of the resin composition lowers at the time of molding, so that the molding becomes unstable, whereby the dimensional accuracy tends to deteriorate. If the average particle size exceeds 7 xcexcm, then irregularities on the order of microns occur when silica particles are precipitated on the surface, whereby the dimensional accuracy tends to lower. Further, the surface area of silica decreases, whereby its strength tends to lower.
Preferably, in the optical fiber positioning member, the content of tetrapod-shaped whiskers in the resin composition is 8% to 12% by weight, 6% to 10% by weight, or 8% to 10% by weight.
Preferably, in the optical fiber positioning member, the total content of silica particles and tetrapod-shaped whiskers in the resin composition is 70% to 76% by weight.
If the total content is less than 70% by weight, then the coefficient of linear expansion of the whole resin composition becomes higher, whereby the dimensional accuracy of the optical fiber positioning member tends to lower. If the total content exceeds 76% by weight, then the fluidity of the resin composition lowers at the time of molding, so that the moldability deteriorates, whereby the dimensional accuracy tends to lower, and the mechanical strength tends to become insufficient.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.